The present invention relates generally to the field of spirometry. In particular, the invention pertains to a device and method for measuring critical portions of an individual spirogram.
Treatment and diagnosis of individuals with chronic lung disease requires measurement of pulmonary function. Treatment of these individuals requires measurement of the pulmonary function on a routine basis throughout the patients' life. These measurements are useful in the day to day management of diseases such as asthma and Cystic Fibrosis. Pulmonary function measurements may also be useful in the conditioning of athletes where training regiments can be optimized to achieve maximum lung condition. A simple device and method has not been available to measure pulmonary functions, other than a peak flow meter. Traditional spirometry has been used to measure various pulmonary function parameters such as forced expiratory volume in one second (FEV1), peak expiratory flow (PF), forced vital capacity (FVC) and forced expiratory flows at 50% and 75% (FEF25:75). Traditional spirometry forces a patient to exert maximal expiratory effort, i.e., exhale as hard, fast and long as possible. Some patients during traditional spirometry procedures may exhale for as long as 20 seconds or more. Such strenuous effort can be painful and fatiguing, particularly for those suffering from pulmonary disease or dysfunction.
Traditional spirometry has several limitations. These include, for example: (1) the start of the "blow" must be established by back extrapolation; (2) the most reliable measurement, the Forced Expiratory Volume in One Second, has an extrapolated beginning and a convenient, but arbitrary, duration; (3) the Peak Expiratory Flow (PF) is an instantaneous measurement and attainment of maximum value compromises the values for the Forced Vital Capacity (FVC); (4) the FVC has a calculated beginning (#1) and end as well as an arbitrary requirement for its duration; (5) efforts to maximize the FVC cause a decrease in the PF; (6) arbitrary criteria are needed to establish the best efforts; (7) the boundary of the forced expiratory flow volume loop is effort independent, i.e., no effort can increase the size of the curve, but all the "normal" and calculated values are dependent on the observed measurement of the FVC; (8) forced expiratory flows are 50% and at 75% expired are arbitrary and instantaneous points whose "normal" and calculated values are dependent on the magnitude of the FVC; (9) the reliability of spirometric test results is comprised in the very young, old, mentally and physically limited subjects; (10) much effort must be expended to calibrate the spirometer to ensure accurate measurements; (11) reference standards and calculations are based on assumptions of water vapor contents of the expired air which many authors have shown to be imprecise; and (12) current instrumentation is expensive.